Image data derived from video is an attractive form of input for computer applications. Advances in low-cost digital imaging have extended the feasibility of this approach to consumer-electronics systems, including video games. Nevertheless, extracting usable input from image data is a complex task. In some cases, the image data may be used to construct a virtual model of one or more physical objects, whose movements or configurations encode the input. However, images of such objects may include optical artifacts, may obscure key features, or, for other reasons, may fail to manifest the input in a straightforward manner.